Have 89 iroc, l98 engine. Started missing the other day. Pulled plugs and found cyl. 4+2 fouled. 4 was bad, but 2 seemed oily. Had valve seals done about a year and a half ago. No oil consumption noted, engine not blowing smoke or running problems till the other day. Am aware of the usual things(rings, seals), but why 2 cylinders with essentially the same prob. TNX, Danno

 

Danno,

Aside from the obvious things you have mentioned, the oil on the #2 could be normal oil that is distributed on the cylinder walls by the rings. If there is no fuel being admitted to that cylinder to create combustion, the oil will tend to collect above the piston and on the plug and chamber surfaces. I had the same thing happen when I had injector problems, and the lack of fuel caused eventual oiling of the plug. The plug was otherwise clean with no carbon or fouling. I chased that probelm around for a while before I determined that the injector was not spraying properly. You might want to unplug the suspect injector and see if the engine RPM or idle quality changes. If not, you may have a problem with that injector.

Just another possibility.

 

Good idea. I did use steth. to check for inj. action. Got a nice strong tick, but nozzle flow could be distorted. Some history- year and a half ago I lost intake manifold gasket at water loop area in front. Dumped coolant into oil. Got it out fast and pulled top end. Had heads gone over by a very reliable machine shop, aside from the usual seals everything looked good. Replaced gaskets at manifold, heads and tpi assy. I left the old plugs in since I had replaced them a couple of months earlier. They are in the same area as where the intake gasket broke. Could they have been contaminated causing erratic operation? They looked OK, but coolant is nasty stuff. Let me run this by you Vader, how about if the new intake gasket is leaking in that area. A leak on the inside facing the pushrod area could draw oil into the cyl. Any info on whether retorking of manifold is needed? Used torque wrench on every nut and bolt along with app. thread sealer. Surfaces were clean when reassembled. Almost threw on alum heads, next door neighbor is a mechanical eng. with an auto shop you have to see to believe. He suggested to stick to stock cast iron. Cannot avoid the problems with mating dissimiliar metals with diff. expansion rates. Anybody know of a better gasket to use if I wind yanking the intake again? Tnx for help Danno

 

Danno,

If the head and intake surfaces were clean, and the heads were not milled as part of the rework, there SHOULD be no sealing problems. Your hypothesis is valid, and if you are losing oil it could be that it is being drawn into an intake runner.

Personally, I would change all the plugs again. The glycol in antifreeze concentrate doesn't evaporate easily, and could be soaked into the insulator of the suspect plug(s), effectively shorting the plug to ground and rendering it useless. Reliable plugs are a must, and the coolant and oil fouling can't be helping the situation. Stick with plain old resistor AC R45TSX or Champion RV15YC4 (my preference only because of plating) in the standard heat range, gapped at the standard 0.035". I anyone is wondering why I keep pushing Champion plugs as opposed to the "politically correct" AC/Delcos, just remember that the '82-'85 Macho T/As came with Champion plugs as part of the upgrade. What was GM telling us with that? Right.

You could also get an indication of the possibility of a vacuum leak by taking a vacuum reading at idle. If it is much below 17" Hg, you may be correct. Another way to test that theory is to create a negative pressure in the crankcase by temporarily pinching or blocking the CCV hose from the throttle body. The PCV system will evacuate the crankcase and force the suspect cylinder draw intake air through the normal intake tract rather than through the lifter area - if the lifter area is in a vacuum the intake system will be the easier path for air to flow. Of course, if there had been constant oil consumption with no apparent leakage, that would be another indicator of a leak, but you noted that oil consumption is not apparent.

Once you feel satisfied that the intake is sealed, you can test the injector theory by using a jumper to manually operate the injector on the suspect cylinder and causing extra fuel flow. If the idle RPM and idle quality improve by dumping the extra fuel, you may have a restricted injector in that position. Note that if there is a vacuum leak, the extra fuel will only serve to correct the fuel mixture as well, so be sure that the intake is sealed by retorquing to the proper 18-20 lb/ft and assuring a good fit.

 

...and if you do get to the point where you suspect and injector, you can try this method to isolate it:

If you are certain the ignition system is functioning and you have good compression on all holes, you need to perform a power balance test to locate the offending cylinder(s). I had a similar problem with my TPI and the test isolated the dead holes.

To perform a power-balance test, start the engine, allow it to reach operating temperature, then unplug the IAC electrical connector while the engine is idling. Unplug the electrical connector from one injector and monitor the engine RPM as it is disconnected. The drop in idle RPM should be relatively equal through the firing order. Replace the electrical connector and go on to the next injector. You need to realize that the ECM will sense the RPM drop and attempt to compensate by adjusting the IAC, which is why it was disconnected in the first place.

Compare the RPM drop at each cylinder. When finished, don't forget to replace the IAC connector. If one or more injectors caused little or no change in RPM, it is not flowing fuel at the correct rate. NOTE: This test will not be accurate if the ignition system is not in good order or compression is low on a cylinder.

This test allowed me to identify two defective injectors, and test results after removal of the injectors confirmed that - two of them had very poor spray patterns and low flow rates. The engine had 18,000 miles and I had already tried several types of injector cleaner in the fuel tank with no improvement. Electrical resistance tests of the injector solenoids revealed nothing outside of the normal 16-17 ohms, further proving my point that injector resistance is not a valid diagnostic tool for determining injector performance or flow unless there has been a complete coil failure, and in fact the cleaned injectors were returned to perfect condition with simple cleaning and flow matching.

As always, if you discover a bad injector, I would recommend contacting Cruzin' Performance.